Fix behavior of stream settings regardless of logging

This pull request fixes behavior of `outputStream` and `errorStream` settings. They are intended for forwarding the stream to a file, not for logging. So they should work even if `logging` is set to false.

Following example saves the kernel log. This should work regardless of logging.

```groovy
ssh.run {
  session(ssh.remotes.localhost) {
    new File('dmesg.log').withOutputStream { stream ->
      execute 'dmesg', outputStream: stream
    }
  }
}
```